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Show 24 F R 0 ST. NoTE XII. many mm· utes ·m t h e a1· r o f a r oom heated fo much above any natural atmofpheric heaCt, do not feem conclu!lve, as they remained in it a Jefs time than would _have b_cen nece - r I 1 t d a mafs of beef of the fame magnitude, and the CJrculatwn of the 1ary to 1ave 1ea e . . · ld blood in living animals, by perpetually bringing new fupphes of flu1d to the flon, wou l t the external furface from becoming hot much fooncr than the whole m~fs. And tphriervdelyn, there appears no power of anu. nal bod .1 es to prod uce. coJ d m· difeafes , as m fcarle. t fever, in which the increafed aClion of the vcffels of the Ibn produces heat and contn-butes to exhao!l: the animal power already too much weakened. . It has been thought by many that fro (ls meliorate the ?r.ound, and that they are.J:1 eneral falubrious to mankind. In refpeCl to the former ltJs.now wdl h.nown that ICC !r fnow contain no nitrous particles, and though fro!l: by enlarging the bulk of mmft clay 1e aves 1· t1r0 ft er Jci0 r a t·1me after the thaw ' yet as foon as the water exh::des , the cl ay b·e co[m, ef s as hard as before, being preffe.;d together by the incumbent atmofphere, and ~y 1ts el - n · lied fetting by the potters. Add to this that on the coafl-s of Afnca, where <~ttrat.:tlOn, ca ;• · f · I f rO1l1l. J• S un known , the fertility of the foil is almo!l: beyond our concept iOns o ·dI t. · n re f peenl to t 11 e genera1 1ra Jubr1"ty of fro!l:y feafons the bills of mort:.t lity . are an ev.1. ence lU the negative, as in long frofls many weakly and old peo~le pe:1fl1 from debi11ty occafioned by the cold, and many clafles of birds and other wild anunals an: benumbed by the cold or deflroyed by the confequent fcarcity of food, and many tender veget:1bks peri01 from the degree uf cold. . .I do not think it fhould be objeCted to this doClrine thot th,ere are m01!l: d:1ys attcnJed with a brifk cold wind \\.-hen no vif1ble ice appears, and which are yet more dif~gr~eablc and dcflrutlive than frofly weather. For on thcfe days the cold moiflure, wluch IS depouted on the fkin is there evaporated and thus produces o deg~ee of cold perhap~ greater than the milder frofls. Whence even in fuch days both the d1fagreeable fenfauons and infalubrious efKCl:s·belong tD the caufe abovementioned, Yiz. the intcnfity of the colJ. Add to this that in thefe cold moifl days as we pafs along or as the wind blows upon us, a new fheet of cold water is as it were perpetually applied to us and hangs upon our bodies, now as water is 8oo times den fer than air and is a much better conductor of heat, we are flarved with cold like thule who go into a cold both, both by the great number of p:trtides in contaCt with the fkin and their gre~ter :;1cility o_f receiving our he_at. It m:~y nevcrthclefs be true that fnows of long duratwn 111 our Wlllte.;rs may be lefs 111- urious to vegetation than great rains unJ !horter fro!ts1 for two reafom. I. Becaufe grea t rains carry do·wn mai1y thoufand pounds worth of the bell: part of th~ manure off the lands ,into the fea, whereas fnow diffolves more gradually and thence cames away lefs from the land; any one may diflioguifh a [now-flood from a rain-flood by the tranfparency of the ·water. Hence hills or fi elds with con!lderaule inclination of furface fh ould be ploughed horiwntally that the furrows m:1y !lay the water from fhowers till it depo!its its mud. z. Snow proteCls vegetables from the fcverity of the frofi, fince it is always in a fi:~te of thaw where it is in contaCl with the earth; as the earth's heat is about 48° and the heat of thawing fnow is 32° the vegetables between them are kept in a d gree of heat ab nit 40, by which many of them are prefcrved. See note on Mufchus, Part. II. of this work. ( '2.5 NOTE XIII.-ELECTRICITY. Coldfrom each point cerulean lujlres gleam. CANTO. I. 1. 339· ELECTRIC POINTS. THERE was an idle difpute whether knobs or points were p.referable on the top of conductors for the defence of houfes. The defign of thefe conduClors is to permit the electric matter accumulated in the clouds to pafs through them into the earth in a fmaller c?ntinued !l:ream ~s . the cloud approaches, before it comes to what is termed fl:riking dlil:ance ; now as It IS well known that accumulated eleCtricity will pals to points at a muc~ greater difl:ance than it will to k;10bs, there can be no doubt of their preference; an~ 1t would feem that the finer the points and the lefs liable to become rufiy the better, as 1t would take off the lightning while it was !l:ill at a greater difl:ance, and by that means preferve a greater extent of building; the very extremity of the point fhould be• of pure filver or gold, and might be branched into a kind of brufh, fince one fmall point cannot be fuppofed to receive fo great a quantity as a thicker bar might conduCl: into the earth. If an infulated metallic ball is armed with a point, like a needle, projeCting from one part of it, the eleClric fluid will be feen in the dark to paf.~ off from this point, fo long as the ball is kept fupplied with eleCtricity. The reafon of this is not difficult to comprehend, every part of the eleCtric atmofphere which furrounds the infulated ball is attracted to that ball by a large furface of it, whereas the electric atmofphere which is near the e.xtremity oft~e needle is attracted to it only by a fingle point, in confequence the partJcl. es of eleetnc ~at.ter near the furface of t~1e ball approach towards it and pufh off by the1r greater gravJtatwn the particles of eleCtric matter over the point of the needle in a continued !l:ream. Something like this happens in refpeCl: to the diffufion of oil on water from a pointed cork, an experiment which was many years ago fhewn me by Or. Franklin; he cut a piece of cork about the fize of a letter-wafer and left on one edge of it a point about a ilxth of an inch in length projeCting as a tangent to the cir~umference. This was dipped in oil and thrown on a pond of water and continued to revolve as the oil left the point for a great many minutes. The oil dcfcends from the floating cork upon the water being diffufed upon it without friCtion and perhaps without coJHaCl; but irs goi ng off at the point fo forcibly as to make that cork revolve in a colitrary direction feems :~nalogous to the departure of the elctlric fluid from points. Can any thing fimil ar to either of thele happen in refpeCl: to the eJrth's :J.tmolphere and give occafi on to the breezes on the tops of mountain s, wl1 ich may be conlldcreJ as points on the earth 's circumference ? D |